Sudan's government on Sunday warned over insecurity in South Darfur state, where rebels said they destroyed an army garrison and the top local official has been replaced by a retired general.
The Sudan Liberation Army's Minni Minnawi faction said they killed an unspecified number of government troops in an attack on the Donki Dreisa base, about 50 kilometres (30 miles) south of the state capital Nyala.
Sudan's army spokesman could not be reached but the latest attack claimed by the rebels came eight days after they began an occupation of Muhagiriya and Labado, two communities about 100 kilometres east of Nyala.
On Saturday, international peacekeepers said the rebels still appeared to be in control of both towns, where thousands of displaced people had sought protection around bases of the African Union-United Nations Mission in Darfur (UNAMID).
Last week, Minnawi rebels also claimed to have moved through Ishma village, 30 kilometres east of Nyala.
Vice President Ali Osman Taha "confirmed the importance of security and stability", justice and rule of law in South Darfur, the official SUNA news agency reported.
Taha made the comments during a meeting with the new South Darfur governor, retired general Adam Mahmoud. He replaced the former civilian governor, Hamad Ismail, who was removed on Friday.
"I am going to make my best effort to have security and stability," SUNA quoted Mahmoud as saying.
In February, a United Nations panel of experts said it had collected testimonies of insecurity, including "growing crime inside towns such as Nyala".
That same month, Darfur's top official Eltigani Seisi told AFP that, except for ethnic tensions in North Darfur state, security in South Darfur and the rest of the region had improved.
Ethnic rebels in Sudan's far-western Darfur area rose up against the Arab-dominated Khartoum government in 2003.
While the worst of the violence has long passed, rebel-government battles continue but instability has been complicated by inter-Arab fighting, kidnappings, carjackings and other crimes, many of them suspected to be the work of government-linked militia and paramilitary groups.
On Sunday, UNAMID said Sudanese authorities blocked the peacekeepers from an area of western Darfur, where at least 50,000 people have fled tribal fighting.
It is the latest of numerous access restrictions cited by UNAMID, despite an agreement with the government which says peacekeepers have freedom of movement.
"The mission is not in a position to provide detailed information about the situation in the Umm Dukhun area as a UNAMID verification patrol, which attempted to gain access on 10 and 11 April, was not allowed to do so by the government of Sudan authorities," UNAMID spokeswoman Aicha Elbasri said.
At least 18 people had been killed in fighting between the Misseriya and Salamat tribes in the area bordering Chad, a tribal leader told AFP last week.
On Saturday in New York, the UN's deputy spokesman Eduardo del Buey said "50,000 people in the last week alone" had fled over the border to Chad because of the inter-tribal conflict.
UN chief Ban Ki-moon said in a January report that UNAMID "continued to call on government authorities to allow it unhindered freedom of movement throughout Darfur", as specified in the written agreement between the two sides.